 (def num-initial-birds 25)
 (def minimum-num-birds num-initial-birds)
 (def num-initial-foods 20)
+(def minimum-num-foods num-initial-foods)
 
 ;; Energies
 (def child-bird-energy-cost 0.15)

               :energy (- (:energy bird) bird-cost-of-living))]
    (when (pos? (:energy bird))
      (if (> (:energy bird) child-bird-energy-cost)
        (list (make-bird (:friendliness bird) (offset-position (:position bird) 2))
              (assoc bird
                :energy (- (:energy bird) child-bird-energy-cost child-birth-energy-loss)))
        bird))))


(defn make-bird
  "Make a new bird with the specified program. At the specified location."
  [genome position]
  (-> {}
      (make-real)
      (make-box)      
